Individual images to flip & form one image

Hey guys, looked around and couldn't find anything on it (trying to word it was difficult too).

I'm looking at having 12 separate comps which show individual videos, all flip at separate times to form one big image.

You know when you look in the crowds of football stadiums and everyone is holding a different sign then they flip them around and when looked at together all the pictures form one massive image like the face of someone or something, I tried doing this individually but failed...any ideas?

Have you looked at the Card Dance plug-in? If you have your 12 videos together in a precomp, Card Dance will let you chop it up into sections (say a 4x3 grid) and then animate each panel separately, with your final image as the back of the panels. You can either make them flip over in sequence, like a finely-tuned North Korean propaganda show, or you can use a gradient map to make more complex transitions. As well as the rotation of each panel, you can control the scale and position, so with a wiggle expression, you should be able to make it look like a heaving crowd.

I was never too clear about the difference between those two plugins, so I just had a look. Card Wipe has a handy Transition slider, which makes it probably an easier choice than Card Dance, which seems to be all driven by gradient maps (although you can use gradient maps in Card Wipe as well).